What is Hypernatremia?

Medical dictionary defines hypernatremia (pronounced: [hahy-per-nuh-tree-mee-uh]) as “a pathological abnormally in which there is high concentration of sodium in the blood” (usually above the value of 145 mmol/L) [1].

Severe cases may register blood sodium values as high as 152mmol/L. On the other hand, serum sodium values slightly lower than 145mmol/L constitute mild hypernatremia. While an increase in blood sodium is a sign of hypernatremia, it is, however, as a result of excessive loss of fluids or water in the body.

When there is a decline in water level in the blood, a concentration gradient is induced which forces sodium ions to migrate from the body cells into the blood plasma through the process of osmosis.

Hypernatremia

Hypernatremia is a common incidence among the elderly, infants and mentally or physically disabled persons since they cannot physically get water on their own whenever they feel thirsty.

ICD 9 code for hypernatremia is: 276.1 [2]

Causes of Hypernatremia

Causes of hypernatremia are typically categorized according to each type.

Common causes of hypernatremia include:

Pseudohypernatremia

This is a false indication of high sodium levels in the blood. It occurs when there is low plasma protein due to an exclusion effect on blood electrolytes thus portraying a rise in sodium in the blood.

Hypovolemic causes

Hypovolemia or hypovolemic shock is a condition that entails decrease in the volume of blood plasma due to prolonged dehydration. Most cases of hypovolemia are due to limited access to regular water intake or excessive loss of fluids from the body. The list below details some of hypovolemic causes of hypernatremia.

Severe losses of water via urine: this is due to certain urinary tract disorders like osmotic diuresis which leads to increased urination. Presence of substances like mannitol or isosorbide in the kidney causes impaired reabsorption of water and sodium.

Excessive loss of water due to prolonged diarrhea. This is common among the elderly and infants. Water is lost directly through watery stool.

Prolonged sweating or perspiration: if a person is exposed to unfavorable weather conditions e.g. dry and hot environment, they will eventually lose a lot of water via sweating causing hypernatremia. Sweat not only leads to direct loss of body water but also important solutes like potassium.

Kidney diseases: many kidney diseases like Nephrotic syndrome induce excessive loss of plasma protein into urine due to impaired renal permeability. This may also be depicted by extensive edema in the body.

Euvolemic causes

As opposed to hypovolemia, euvolemia is a biological condition in which there is a decrease in total body water without an associated decrease in sodium levels (i.e. sodium level remain relatively constant while there is a drop in free water in the body). Such a condition may be cause by one or more of the following:

Sweating

Nephrogenic diabetes insipidus due to either limited production of vasopressin or slow response to hormone vasopressin

Loss of appetite: this is common among the aging group. Acute loss of water (dehydration) causes massive thirst which makes one sad leading to loss of appetite.

Confusion: Inadequate free water in the blood impairs normal brain function making one disoriented and unable to think or reason well. Brain cells require both sodium and water to function normally.

Fatigue: this is experience because muscles cannot function well without water. Since water is an essential input into metabolic process, a dehydrated people tend to exhibit signs of tiredness [3,4,5]

Diagnosis of Hypernatremia

As rule of thumb, a physician must start the diagnosis by establishing patient’s medical history for any past case of hypernatremia or related disorders. Since a rise of blood sodium (above 145mM) is a clear indicator of hypernatremia, it is necessary to obtain a laboratory workup of the following:

Blood levels of important electrolytes like sodium, potassium or calcium ions

Urinalysis for any defective hormones and levels of electrolytes/water. Also to get hour-to-hour urine volumes

Osmolality of both urine and blood plasma

Water deprivation test can be carried out for patients suspected to have diabetes insipidus to establish both renal/pituitary responses.

Hypernatremia Calculation and Correction

The following formulas are used to calculate the degree and extend of hypernatremia in a patient: [4]

The calculated change in serum sodium is used to gauge if a patient has hypernatremia or not.

The desired sodium in a human body is about 120 meq/L and the insensible water loss should be between 500 and 1500 cc per day.

Treatment of Hypernatremia

General treatment of hypernatremia require cautious uptake of water into the body with an associated decrement in serum sodium. The rate at which hypernatremia can be corrected depends partially on age and weight of the patient, extend of dehydration, and the nature of the cause itself.

If hypernatremia is rectified too quickly it may cause seizures or brain damage (edema) which can lead to an eventual death.

Figure 2: Management of Hypernatremia (Approach and Algorithm)

The list below details some of the corrections recommended for treatment of hypernatremia:

Oral intake of water: this is the case for patients with small water deficit

Use of hypotonic fluid: a patient should receive a hypotonic fluid that is lower in the concentration of electrolytes. This method would correct impaired removal of sodium in the kidneys. The fluid administered should be hypotonic to the urine.

Administration of insulin: This is used if the primary cause of hypernatremia is diabetes insipidus. Insulin would allow proper production of hormone vasopressin. Therefore, the body can respond timely to vasopressin normalizing sodium/potassium excretion and intake of free water into the body. In addition, any drugs which may cause worsening of diabetes insipidus should be discounted if possible. Such drugs include those that have lithium in them.

Dialysis: this may be required to correct such causes of hypernatremia as heart failure and edema (pulmonary).

IV therapy: if water deficit very large, a patient may need to have water and other important electrolytes administered through intravenous methods. IV therapy involves two phases: emergency phase and rehydration phase.

Emergency phase entails use of a neutral (isotonic) fluid to replenish blood plasma volume. Fluids such as Ringer solutions which contain sodium and other electrolytes can be used as the replenishment fluid. Amount and concentration of the fluid depends on the age and weight of the patient.

In the rehydration phases, a hypotonic fluid is used. Such a solution normally contains some dextrose sugar, normal salinity and around 31mM of sodium. In this phase, the body is supposed to replenish its blood free water supply by creating an electrolyte concentration gradient that favor uptake of water into the blood plasma [3, 4, 5]